1. Field of the Invention
The present invention relates to carrier substrates and, more particularly, to a carrier substrate having an array of contact arms disposed on a PCB side of the carrier substrate and a chip module using the same. The invention is further concerned with a method of fabricating the inventive carrier substrate.
2. Description of the Prior Art
As the input/output (I/O) pin count and circuit density of the integrated circuit (IC) chip continue to increase, the process of bonding or mounting a chip module onto a printed circuit board (PCB) becomes a big challenge. Typically, the chip module is directly mounted on the PCB by soldering such as ball grid array (BGA). However, such connections made by soldering are not reversible and the cost is high when replacement of the chip module is required after assembly.
To cope with the problem, an interposer connector or interposer has been developed, which is interposed between a chip module and a PCB. As shown in FIG. 1, an interposer 3 is disposed between a carrier substrate 1 and a PCB 2. The interposer 3 includes a substrate 30, a plurality of flexible contact members 32 mounted on a chip mounting side or chip side 3a of the substrate 30, and a plurality of solder balls mounted on a PCB side 3b of the substrate 30. The flexible contact members 32 electrically contact the land grid array (LGA) pads 12 on the bottom side 1a of the carrier substrate 1. The solder balls 34 are electrically connected to the PCB 2.
The above-described prior art has several drawbacks. For example, the assembly of the aforementioned interposer is more complex and is thus more expensive. Further, the interposer between the chip and the PCB increase the signal transmission distance, whereby reducing the device performance. Besides, the interposer increases the total thickness of the circuit board assembly and is therefore not feasible for some applications for which the assembly space is limited.